The present invention relates to an internal combustion engine, especially for a portable, manually-guided implement such as a power chain saw, a cut-off machine, a brush cutter or the like. The engine has a cylinder and a crankcase, with a reciprocating piston in the cylinder that together with the cylinder delimits a combustion chamber. The piston drives a crankshaft that is rotatably mounted in the crankcase. A diaphragm carburetor is provided for supplying a fuel/air mixture for operation of the engine, whereby the carburetor has a control chamber that is delimited by a control diaphragm and to which fuel flows via a feed valve that is controlled by the control diaphragm. A compensation chamber is formed on the dry side of the control diaphragm.
An internal combustion engine of this type is known from DE 199 00 445 A1. The fuel/air mixture is drawn into the crankcase and, as the piston moves downwardly, is conveyed into the combustion chamber via transfer channels. To reduce the scavenging losses, in particular the transfer channels that are disposed close to the exhaust communicate via diaphragm valves with air channels that supply clean air, so that the rich mixture is shielded from the exhaust or outlet means by the in-flowing air. This known engine has a good exhaust gas characteristic at low fuel consumption.
The drawback is that such an engine operates leaner under full load and reduced speed, since in such an operating state an over proportional amount of air that is free of fuel is supplied via the air channels. The power of the engine drops, which can lead to a further reduction in speed.
It is therefore an object of the present invention to improve an internal combustion engine of the aforementioned general type in such a way that a powerful output is ensured even at a speed that drops under full load.